With rapid increases of city electricity consumption, higher demands on the reliability of electricity consumption are imposed, especially in important occasions such as elevators, fire control, hospitals, subways, communication where power supply should not be cut off, the reliability of a persistent power supply is of particular importance. For the important occasions above, a dual power switch is generally adopted to ensure a persistent and uninterruptable power supply. The dual power switch is mainly used for switching between power sources of master devices. Typically, a main loop of a load side is generally connected with a main power source side. When power outage occurs due to failure of the main power source side, the dual power switch may automatically connect the main loop of the load side with a backup power source side, so as to achieve the purpose of allowing the load side to supply power uninterruptedly.
However, existing dual power switches generally adopt direct switching of the first/second position electrodes, that is, there are only two states. If the circuit needs maintenance or a circuit device needs to be installed, it is difficult to ensure that the circuit keeps a completely cut-off state. Moreover, conventional double-power linear-motion switches use the elastic force of an energy-storage spring to return a movable electrode to an intermediate open position, as shown in FIG. 1. After the movable electrode 71 is released from a position at which it comes into contact with fixed electrodes 75, the movable electrode 71 makes a reciprocating movement under the effect of a right energy-storage spring 73 and a left energy-storage spring 72. The movable electrode 71 has to make multiple reciprocating movements before stopping at the intermediate open position by its own inertia, which takes a long time, and the open-circuit reliability is low.